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neurophys1,2

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2018-04-17 10:45:39 -07:00
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neurophysiology2.md
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Note:
<!-- ## Feedback cycles responsible for membrane potential changes
<div><img src="figs/Neuroscience5e-Fig-03.09-0_0ffcd53.jpg" height="100px"><figcaption></figcaption></div> -->
@@ -366,7 +367,7 @@ Note:
<div></div>
* Question– Why do APs exhibit an all-or-nothing threshold?
* Answer– When membrane potential (V<sub>m</sub>) is below threshold there is not enough Na⁺ channels open to raise V<sub>m</sub> high enough to open more channels. When V<sub>m</sub> is above threshold the action potential cycle is activated.
* Answer– When membrane potential (V<sub>m</sub>) is below threshold there is not enough Na⁺ channels open to raise V<sub>m</sub> high enough to open more channels. When V<sub>m</sub> is above threshold the 'explosive' action potential cycle is activated.
* Question– Why to APs exhibit an undershoot?
* Answer– During the AP voltage-gated K⁺ conductance slowly increases (delayed activation of voltage-gated K⁺ channels) and during the falling phase these K⁺ channels are still open and active whereas voltage-gated Na⁺ channels are inactivated… as V<sub>m</sub> approaches E<sub>k</sub> there is briefly more K⁺ flowing out than at rest and the hyperpolarization inactivates voltage-gated K⁺ channels. K⁺ leak channels and ion transporters bring back cell to resting potential.
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bottom graph shows the peak Vm
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<!--
## Action potential conduction requires both active and passive current flow
@@ -433,10 +434,8 @@ bottom graph shows the peak Vm
<div><img src="figs/Neuroscience5e-Fig-03.10-3R_d3311ca.png" width="500px"><figcaption>Neuroscience 5e Fig. 3.10</figcaption></div>
<!-- <div><img src="figs/Neuroscience5e-Fig-03.10-4R_03ef878.png" width="200px"><figcaption>Neuroscience 5e Fig. 3.10</figcaption></div> -->
Note:
<div><img src="figs/Neuroscience5e-Fig-03.10-4R_03ef878.png" width="200px"><figcaption>Neuroscience 5e Fig. 3.10</figcaption></div>
Active and Passive current flow.
@@ -445,6 +444,8 @@ Active and Passive current flow.
* Local passive depolarization causes nearby Na chan to open and another AP is generated
* Na chan upstream inactivate and K chan open. Vm repolarizes and is refractory to further AP generation upstream
* Process repeated downstream, propagating AP along the axon
-->
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@@ -502,27 +503,26 @@ Note:
Note:
saltatory action potential condution along a myelinated axon
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<!--
## Nodes of Ranvier
<div><img src="figs/Neuroscience5e-Fig-03.11-0-crop_d8af80c.jpg" height="500px"><figcaption>Neuroscience 5e Fig. 3.11</figcaption></div>
<div><img src="figs/Neuroscience5e-Fig-03.10-4R_03ef878.png" width="300px"><figcaption>Neuroscience 5e Fig. 3.10</figcaption></div>
Note:
saltatory action potential condution along a myelinated axon.
red indicates imaged expression of voltage gated Na channels. green indicates a protein (Caspr) associated with the nodes of Ranvier.
-->
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## Speed of action potential conduction in unmyelinated versus myelinated axons
<div><img src="figs/Neuroscience5e-Fig-03.12-0_214d611.png" height="500px"><figcaption>Neuroscience 5e Fig. 3.12</figcaption></div>
<div><img src="figs/Neuroscience5e-Fig-03.12-0_214d611.png" height="450px"><figcaption>Neuroscience 5e Fig. 3.12</figcaption></div>
Note:
@@ -592,5 +592,3 @@ ultimate cause of MS remains unclear. Immune system contributes to damage and is
* women to men ratio 3/2
* Genetic component is likely the effect of multiple genes
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